At first, critics likely upset if shown Finding Nemo? (9)

'nemo?' is the definition.
(Nemo from the film Finding Nemo is a clownfish)

'at first critics likely upset if shown' is the wordplay.
'at first' says to take the initial letters.
'upset' indicates anagramming the letters.
The first letters of 'critics likely' is 'cl'.
'if'+'shown'='ifshown'
'ifshown' with letters rearranged gives 'ownfish'.
'cl'+'ownfish'='CLOWNFISH'

'finding' is the link.